The present invention relates to robotics systems for use in automated laboratory applications, and more particularly to a liquid separation device which is particularly well suited for such applications as automated analytical laboratory systems. Frequently, for example, immiscible liquids must be separated from a container, such as a test tube, but the volumes of the liquids to be separated are unknown. The present invention detects when the removal device has concluded withdrawing the target liquid independently of the volume withdrawn or the time required therefor.
Automation in analytical laboratories is not, of itself, a new concept, but instead has been widely practiced for many years. More recently, it has appeared mainly in the form of microprocessor-controlled analytical instrumentation with dedicated hardware, such as auto samplers, continuous flow systems, and computerized data collection, calculation, and report generation facilities. The very recent past has seen important improvements wherein laboratory automation has been extended by the use of robotics, combined with programmable computers, to new tasks which include sample preparation, and even entire analytical determinations. The first such robotic system was introduced in 1982 by Zymark Corporation (Hopkinton, Mass.). As experience has been gained with these systems, they have been successfully applied to ever more sophisticated laboratory operations, and the number of accessory components for specific tasks has grown accordingly. Understandably, however, there continues to be a great need for accessory modules and equipment which can provide sophisticated support operations in a robot-friendly manner. Tasks which are so trival for a human operator that they go essentially unnoticed may prove to be all but insurmountable for a robotics system. Sometimes the most trival and routine manual operations turn out to be the most intransigent when efforts are made to perform them with robot-friendly modules and sensors. As a result, modules and sensors for performing many important tasks are still not yet commercially available.
An example in which accessories are available, but which have certain very definite limitations, has to do with withdrawing or removing liquids from a vessel such as a test tube, in the presence of other usually immiscible liquids. Due to differences in density, the liquids will ordinarily be separated. With a typical prior art system, a photocell will be positioned at the height down to which the heavier liquid is to be drawn. A cannula is then inserted down at least to that level and the heavier liquid is withdrawn through the cannula until the optical sensor detects a change in the optical characteristics of the liquid. This approach, which can also be used with a common solvent where separation has been achieved with centrifugation, is very effective, reliable, and relatively inexpensive when the respective liquids have distinguishing optical properties such as color and/or opacity. When such differences are absent, it is often convenient to add a selectively soluble dye so that adequate differences in optical properties can be artificially but harmlessly provided.
Of course, this still leaves a great number of situations in which optical separation is either inconvenient, or in some cases all but prohibited, due to the circumstances involved. In such cases, particularly when dealing with immiscible liquids, the interface between the liquids will usually be readily visible to a human operator, but the task is then anything but trivial for a robotics system.
A need therefore remains for a robotic separation sensor for use in combination with a cannula liquid delivery system for detecting when a liquid being delivered through the system is changed to another type of liquid, independently of such properties of the liquid as volume, viscosity, optical characteristics, or the time required for the liquid to be delivered. Such a system should accurately detect when the liquid has been withdrawn from the target container to the desired level, preferably based on the actual properties of the liquids involved in the procedure, without alteration such as the addition of foreign substances (dyes, etc.).